1. Field of the Invention
This invention relates to a method for producing a blow molding tube or tubes having a large thickness flange injection molded at an end of the tube.
2. Prior Art
Methods for producing such a tube with an end flange are disclosed in Japanese Patent Application Laid-Open 104815/1988 and Japanese Patent Application Laid-Open 290715/1988.
In the method disclosed in the former publication a, molding material or parison is extruded so as to be longer than the blow molding die assembly. And, when a mandrel is forced into the die assembly from one end thereof, the longish portion of the molding material is squeezed so as to form an integral flange at the tube end.
The method disclosed in the latter publication, has been developed earlier by the present applicant. In this method, a blow molding tube is inserted into an injection molding die assembly while it is not yet cooled down after blow molding, and a flange portion is formed by injection molding so that the injection molding flange is integral with the blow molding tube.
In the former method, however, the upper limit of the obtainable thickness of the flange is about the same to 1.5 times that of the molding material or parison. Therefore, the method is not suitable for producing a tube with a large thickness flange such as an engine intake manifold shown in FIG. 11, which is used in an automotive engine room.
The latter method is superior in its thermal efficiency. However, molten resin is liable to leak through the gap between the blow molding tube and injection molding dies at the time of the injection molding, thus resulting in a defective molded product.